Floppy disk unit

ABSTRACT

A floppy disk unit rotates a recording medium loaded thereon and reads information from or records information on the medium with magnetic heads. A bearing for rotatably supporting the medium includes a bearing member made of sintered alloy, and the member is formed with a band-like projection along the edge of its end portion. A metal support plate has a through hole perforated by press work or the like and a portion formed along the edge thereof, which is larger in diameter than the rest of the through hole and provides a gap between the through hole and the end portion of the bearing member fitted therein. The band-like projection is caulked and fills up the gap to be substantially flush with the support plate, thereby fixing the bearing member to the support plate. Thus, the whole unit is reduced both in height and weight, and the manufacturing cost decreases. The unit is provided with an adjustment portion for adjusting beforehand portions of the magnetic heads with respect to the medium. The adjustment portion is arranged in a position where it is prevented from being vertically overlapped with the loaded medium so that adjustment of the unit can be performed from above easily and reliably in stable manner.

BACKGROUND OF THE INVENTION

The present invention relates to improvements in a floppy disk unitwhich is to be used as an external storage device such as a personalcomputer and word processor.

Electronic equipments such as a personal computer having been made morehighly efficient and smaller increasingly in recent years. With thistendency, it is demanded that floppy disk units are made further smallerin size and produced at a lower cost. Concerning the dimensions of afloppy disk unit, there is a limit in miniaturization of the shape inplan on account of the standardized dimensions of a recording mediumthat is called a floppy disk or diskette. On the other hand, height ofthe unit greatly depends on a magnetic head, a driving mechanism, afloppy disk loading/unloading mechanism and a rotary driving device sothat these components are considered as the object of improvement forrealizing the miniaturization.

The rotary driving device of the floppy disk unit generally adopts anoilless metal of powdered sintered alloy as a bearing member. Theoilless metal is press-fitted in a holder or housing of a bearingportion and, thereafter, subjected to sizing work to meek requireddimensions. The oilless metal is suitable to make the floppy disk rotatein stable manner, and however, in order to provide a holding force largeenough to tolerate the sizing work by press-fitting, a certain length isneeded, with the result that the bearing portion is prevented from beingmade smaller in size. Examples of the sizing work for electric motorsare seen in, for instance, Japanese Utility Model Unexamined PublicationNos. 62-54584, 64-23767 and 64-35532.

Further, in order to keep compatibility, it is necessary for the floppydisk unit to adjust the position of magnetic heads with respect to thefloppy disk at the manufacturing stage. The floppy disk unit is providedwith an adjustment portion for this purpose. Heretofore, for therotating position of the floppy disk, an alignment medium has been usedin which the angle is represented by time and a reference signal foradjustment called "index burst" or "time burst" is written, andadjustment has been effected by loading this medium in the floppy diskunit. In other words, the timing adjustment has been effected by theadjustment portion in response to the signal read out from the alignmentmedium.

In general, the floppy disk unit is constructed such that a motor and amotor driving electric circuit are located under the disk or medium. Theabove-described adjustment portion is usually provided on the motordriving circuit so that access to this adjustment portion must be madefrom below the unit. On the other hand, in the manufacturing line, sinceit is efficient and accurate to carry out a job from above the unit,connecting pins for power supply and signals are connected to connectionterminals of each unit from above so as to make each magnetic head moveto a required track of the alignment medium to read the signals. In thisway, in accordance with the readout signals through the connecting pinsconnected from above, the adjustment portion is operated from below tothereby effect the index adjustment.

However, if the adjustment portion is located in a position where it isoverlapped with the loaded alignment medium as described above, theconnecting pins have to be handled from above while the adjustmentportion must be adjusted from below. This gives rise to the followingproblems. Since the adjusting operation is usually performed in a statethat the floppy disk unit is put on a pallet, it is necessary to form ineach pallet a hole for adjustment to be performed from below. Further,an adjusting tool, for example, a screw driver, must be inserted througha small hole formed in a circuit board so as to be engaged with theadjustment portion, and however, this engagement is not easy and hencethe adjusting operation cannot be performed smoothly.

As another prior art, there has been known a floppy disk unit in whichan adjustment portion for index signal is so provided as to face upwardfor the purpose of making it possible to perform the adjustment only bythe operation from above. Such a unit is seen in, for example, JapaneseUtility Model Examined Publication No. 4-37338. However, this adjustmentportion is adapted to detect not the alignment medium but the rotationalposition of the rotor of a motor.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of the problemsdescribed above, and an object of the invention is to provide a floppydisk unit which can be reduced in height and cost.

Another object of the invention is to provide a floppy disk unit whichmakes a bearing portion thinner and has substantially no projectingportion for fixation of the bearing portion to enable reduction ofheight of the unit and which can decrease the number of manufacturingsteps and the number of component parts to be reduced in cost andweight.

Still another object of the invention is to provide a floppy disk unitin which the aforesaid adjusting operation can be performed easily andreliably and which does not involve an increase of cost.

A further object of the invention is to provide a floppy disk unit inwhich a thin bearing portion is provided so as to make the overalldimension of the unit smaller and the adjusting operation can beperformed easily and which can be improved in quality and reduced incost.

To achieve the above objects, the invention is intended to fix anoil-impregnated metal bearing member by means of caulking to provide anecessary holding force and to arrange an adjustment portion in a properposition where access thereto is not hindered by a loaded medium toenable the adjustment operation to be performed from above easily andreliably in stable manner.

According to an aspect of the invention, a floppy disk unit for rotatinga medium loaded thereon to read and write information comprises bearingmeans for rotatably supporting the medium and a metal support plate. Thebearing means includes a bearing member made of sintered alloy, and thebearing member has an end portion and a band-like projection formedalong the edge of the end portion. The support plate is formed thereinwith a through hole in which the end portion of the bearing member isfitted with the projection thereof projected out from one of surfaces ofthe support plate, the through hole has a large diameter portion alongan opening edge thereof in the one surface, which is larger in diameterthan other portions of the through hole, so that the large diameterportion provides, between the through hole and the end portion of thebearing member fitted therein, a gap in which the band-like projectionis caulked and fills to fix the bearing member to the support plate.

With the above structure, by caulking the band-like projection of thebearing member to fill the gap between the bearing member and thethrough hole of the support plate with the caulked projection, thebearing member is fixed to the support plate and a holding forcenecessary for sizing work can be produced. Press-fitting and a lengththerefor are not required so that the length of the bearing member and,therefore, the height of the bearing portion can be reduced. Further, noscrew or bolt is required to fix the bearing member so that the bearingportion has only a few projections. As a result, it is possible to makethe whole unit thinner and, owing to reduction in the number of workingsteps and the number of component parts, the unit can be reduced both incost and in weight.

It is preferred that the through hole of the support plate is formed bypress work and a shear-droop or roll-over portion caused as a result ofthe press work serves as the large diameter portion of the through hole.The through hole and the large diameter portion thereof can be formed ata time, and the working process is further simplified.

Preferably, the dimensions of the projection of the bearing member andthe size of the large diameter portion of the support plate, that is,the amount of the material to be caulked and the volume of the voidspace for receiving it are so set as to make the projection after beingcaulked and the one surface of the support plate substantially flushwith each other. Substantially no projecting portion is resulted fromfixation of the bearing member is nearly extinguished, thereby enablingthe unit to be made further thinner.

It is preferred that the bearing means includes a ball bearing and afitting hole for the ball bearing is formed in the opposite end portionof the bearing member. The bearing member serves as a housing or holderfor retaining the ball bearing as well so that the number of componentparts can be further decreased. In this case, the bearing member ispreferably made of a copper-base sintered alloy. It is easy to attainthe dimensional accuracy with the copper-base sintered alloy so that thedegree of concentricity between the bearing fitting hole and the bearingmember can be increased to improve the accuracy of deflection of thebearing.

It is preferred that the support plate is made of a magnetic material,that is, either iron or silicon steel, and a circuit board is providedon the one surface of the support plate. The number of component partsof a rotary driving system is further decreased, thereby enabling afurther reduction in the cost of the unit.

According to another aspect of the invention, a floppy disk unit forrotating a medium loaded therein to read and write information comprisesrotary driving means for rotating the medium in engagement therewith,magnetic head means provided movably with respect to the medium forreading and writing information, and adjust means for effecting timingadjustment of index signal. The adjust means is arranged to be preventedfrom being overlapped with the medium engaged with the rotary drivingmeans as viewed in plan.

With the above structure, access to the adjust means is not hindered bythe loaded medium, and accordingly, timing adjustment of index signalcan be performed easily and reliably in stable manner.

Preferably, support means is disposed below the medium loaded in theunit, a portion of the support means extends to a position where it isprevented from being overlapped with the medium as viewed from above,and the adjuster means is mounted on the extended portion of the supportmeans. All access to the unit including access to the adjuster meansand, further, electrical connection to the unit can be performed fromabove the until, and accordingly, it is possible to improve the qualityof and reduce the cost of the floppy disk unit.

It is preferred that the medium is loaded to be close to one side in achassis of the unit so as to provide an empty space on the other sideand the adjust means is disposed in this empty space.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing a floppy disk unit according to anembodiment of the invention;

FIGS. 2a and 2b show essential portions of a bearing of the unit of FIG.1, in which FIG. 2a is a sectional view showing a state before a bearingmember is fixed to a support plate and FIG. 2b is a bottom view of thesame;

FIG. 3 is a sectional view showing the essential portions of the bearingof FIG. 2a in a state that the bearing member is fixed to the supportplate;

FIG. 4 is a sectional view showing essential portions of a bearing of afloppy disk unit according to a second embodiment of the invention in astate before the bearing member is fixed to the support plate;

FIG. 5 is an enlarged view showing a part of the essential portions ofthe bearing of FIG. 3;

FIG. 6 is a sectional view showing the essential portions of FIG. 4 in astate that the bearing member is fixed to the support plate;

FIG. 7 is a sectional view showing, on an enlarged scale, the essentialportions of the bearing of FIG. 4 produced by way of trial; and

FIG. 8 is a sectional view showing essential portions of a bearing of aconventional floppy disk unit.

DESCRIPTION OF EMBODIMENTS

Referring to FIG. 1, the floppy disk unit according to an embodiment ofthe invention is generally denoted by reference numeral 1, and it isshown in the state that an index adjusting alignment medium 2 has beenloaded therein. The medium 2 is of a structure that a rotating recordingdisk is received in a jacket and has the same shape as a so-calledworking medium used for write/read or, in the illustrated embodiment, a3.5 inch floppy disk.

The floppy disk unit 1 has a flat box shaped chassis 3 which forms theouter covering of or defines the contour of this unit, and variouscomponent parts are installed in this chassis. The chassis 3 includes afront panel 4 in which an insertion entrance 5 for the medium 2 isformed. A metal support plate 6 is attached to the inside of the chassis3 and a spindle motor 7 serving as a rotary driving device is mounted onthis support plate. On the support plate 6, a circuit pattern of a motordriving system (not shown) is formed through a resin layer (not shown)and circuit components of the motor driving system (not shown) aremounted. The motor 7 has a rotary shaft 8, and a connecting member 9 tobe engaged with a hub of the medium 2 is so provided as to be rotatedwith the shaft 8.

A holder and a driving mechanism (both not shown) for the medium 2 areprovided operatively in the chassis 3. As the medium 2 is insertedthrough the insertion entrance 5, it is received by the holder.Subsequently, the driving mechanism is operated to move forward towardthe insertion entrance 5 to make the holder and the medium 2 come downuntil the hub of the medium 2 is engaged with the rotary shaft 8 and theconnecting member 9 of the spindle motor 7. Conversely, when the drivingmechanism is operated to move back, the holder is caused to go up withthe medium 2 so that the hub of the medium 2 is out of the engagementwith the rotary shaft 8 and the connecting member 9 of the motor 7, andthen, the medium 2 is pushed out so that it is partially projected outfrom the holder and the insertion entrance 5. The holder and the drivingmechanism are arranged such that the medium 2 is located close to oneside in the chassis 3 while an empty cavity or space 10 is formed on theother side in the chassis 3. The holder and the driving mechanism mayhave the same structures as those of the prior art, and therefore, nofurther description thereof will be made herein. Such a holder is shownin Japanese Patent Unexamined Publication No. 4-195762 which isincorporated herein by reference.

The chassis 3 is further provided therein with a head support device 11and a head positioning deice 12. The device 11 is arranged in thedirection crossing the longitudinal axis of the medium 2 loaded in theunit, while the device 12 is arranged in the room or empty space 10along the direction in which the medium 2 is to be loaded and unloaded.

The head support device 11 comprises an elongated carriage 13, a guideblock 14, a head arm 15 and a roll plate 16. The carriage 13 extendssubstantially at a right angle to the direction in which the medium 2 isto be loaded and unloaded, with the free end of the carriage lying abovethe longitudinal axis of the medium 2 and its basal and lying in theempty space 10. The head arm 15 also extends along the carriage 13likewise. The guide block 14 is fixed to the basal end of the carriage13, and the head arm 15 is also attached at the basal end thereof to theguide block 14 through the roll plate 16. The roll plate 16 is made of aleaf spring so that the head arm 15 is pivotally movable up and downabout the guide block 14. A first magnetic head 17 for side 0 isattached to the upper surface of the free end of the carriage 13 and asecond magnetic head 18 for side 1 is attached to the lower surface ofthe free end of the head arm 15, so that both magnetic heads are opposedto each other. The head arm 15 and the second magnetic head 18 arepushed toward the carriage 13 and the first magnetic head 17 by means ofa load spring 19.

The head positioning device 12 comprises a stepping motor 20 and a leadscrew 21. The stepping motor 20 is mounted in the corner within thechassis 3, and the lead screw 21 is rotatably supported by supports 22,23 and extends along the side of the chassis 3. The lead screw 21 isformed in one united body with the rotary shaft of the motor 20, and theguide block 14 of the device 11 is engaged with the intermediate portionof the lead screw 21. A guide plate 24 is fixed to the bottom of thechassis 3, and the free end of the carriage 13 is engaged with the lowersurface of the guide plate 24. The carriage 13 is normally pushedagainst the guide plate 24 by means of a resilient member (not shown) soas to be prevented from rotating about the guide block 14. As the motor20 is driven to rotate the lead screw 21, the guide block 14 is movedalong the lead screw 21 to move the carriage 13 and the head arm 15horizontally. Thus, the first and second magnetic heads 17, 18 are movedin the radial direction of the rotating disk of the medium 2.

When the holder goes up as mentioned before, the head arm 15 and thesecond magnetic head 18 are rotated upwards against the load spring 19not to be in contact with the medium 2. When the holder comes down, thehead arm 15 is rotated downward by the righting elasticity of the spring19 and the medium 2 is held between the first and second magnetic heads17, 18.

Here, description will be made on improvements of the spindle motor 7which is the rotary driving device. First to give a clear understandingof the improvements by the invention, FIG. 8 will be referred to.

FIG. 8 shows essential portions of a conventional spindle motor. Thismotor has a flanged cylindrical housing 201. The housing 201 is fittedin a hole formed in a support plate 206 and fixed to the support platewith screws 202. A ring-shaped partition 203 is formed integrally withthe inner wall of the housing 201 to divide the hollow portion of thehousing into upper and lower parts. A ball bearing 204 is press-fittedin the upper hollow portion of the housing with its outer race fixedthereto, while an oil-impregnated metal 205 is press-fitted in and fixedto the lower hollow portion of the housing. A rotary shaft 208 isrotatably supported by the ball bearing 204 and the oil-impregnatedmetal 205. A bush 207 is fixed to the upper portion of the rotary shaft208, and a rotor (not shown) is attached to the bush. Further, magnets(not shown) are attached to the inner peripheral surface of the rotor.On the other hand, a stator (not shown) is provided on the outerperiphery of the housing 201 and a wound coil (not shown) is attached onthe stator. Similar ones to the conventional structure described oneseen in, for example, Japanese Patent Unexamined Publication Nos.4-147470 and 5-41012.

The spindle motor, when an electric current is passed through thewinding coil of the stator, rotates the rotor, the bush 207 and therotary shaft 208 through the magnets of the rotor. With this rotation,the disk of the medium 2 engaged with the end of the rotary shaft 208 isrotated.

As described above, the oil-impregnated metal 205 is fixed to thehousing 201 by press-fitting. Then, sizing is effected on the metal toattain required dimensions. Accordingly, as it is necessary to provide,through the press-fitting, a holding force larger than a turning momentexterted at the time of the sizing work, the length of theoil-impregnated metal 205 cannot be decreased. Additionally, the headportion of each screw 202 projects down, making it difficult all themore to lessen the overall thickness of the floppy disk unit. Asconcerns fixation of the housing, flush head screw may be used in placeof the round head screws 202 to prevent the head portions of the screwsfrom projecting out from the support plate. In this case, however,counter sinks must be formed in the support plate 206, resulting in anincrease of the number of working steps. In any case, the number ofcomponent parts is large, the cost is high and the weight is heavy.

In the embodiment of the invention, as shown in FIG. 2a, the metalsupport plate 6 is formed therein with a through hole or fitting hole 60by means of press work in such a manner that the hole 60 has ashear-drop or roll-over portion 61 caused along its periphery or openingedge in the lower surface of the support plate, namely a portiondeformed in the edge of the hole as a result of the pressing by a boringtool. On the other hand, a bearing member 70 for the spindle motor 7 ismade of an oil-impregnated metal of sintered alloy, and it has in itsupper part a large diameter portion 71 which has an outside diameterlarger than the diameter of the fitting hole 60, and in the lower partthereof a small diameter portion 72 which is to be fitted in the fittinghole 60. Further, a projection 73 serving as a caulking portion isformed at the lower end of the small diameter portion 72, a through hole74 is formed in the center of the bearing member, and the bearing member70 presents a stepped cylindrical shape as a whole. The caulking portion73 is formed integrally with the small diameter portion 72 and, as shownin FIG. 2b, not only extends along the edge portion of the end face ofthe small diameter portion 72 in the form of a band or, in thisembodiment, in the form of a ring but also projects down therefrom. Theouter periphery of the band-like or ring-like caulking portion 73extends straight so as to be coextensive with the outer peripheralsurface of the small diameter portion 72, while the inner peripherythereof is inclined so as to increase the diameter as going downward.The angle α of this inclination is set to be an acute angle smaller than90 degrees.

When fixing the bearing member 70 to the support plate 6, the smalldiameter portion 72 is first fitted in the fitting hole 60 and the largediameter portion 71 rests on the upper surface of the support plate 6.Subsequently, the ring-like caulking portion 73 is caulked radiallyoutwardly by means of for example a rotary caulking machine to fill upgroove-like gap or a void space 62 between the shear-droop portion 61and the small diameter portion 72 as indicated by chain line in FIG. 2aand, further, as shown in FIG. 3. In this way, the bearing member 70 isfixed to the support plate 6. Thereafter, the rotary shaft 8 isrotatably supported by the through hole 74 of the bearing member 70.

In the floppy disk unit having the above-described structure, as thealignment medium 2 is inserted through the insertion entrance 5 into theholder as indicated by an arrow A in FIG. 1, the aforesaid drivingmechanism is operated to advance to move the holder down, and the hub ofthe medium 2 engages with the rotary shaft 8 and the connecting portion9 of the spindle motor 7. At the same time, a shutter of the jacket ofthe medium 2 is opened so that the first magnetic head 17 of thecarriage 13 is brought into contact with the recording disk through thisopening. Further, as the holder goes down, the head arm 15 is lowereduntil the second magnetic head 18 is brought into contact with therecording disk of the medium 2 through the opening. Then, the spindlemotor 7 rotates the recording disk, and the stepping motor 20 rotate thelead screw 21 to feed or move the first and second magnetic heads 17, 18in the radial direction of the recording disk by pitches of therecording tracks, thereby making it possible to read signalsmagnetically. In the case of a working medium or a floppy disk, it ispossible to write or read signals by means of the magnetic heads 17, 18.

In the embodiment, the floppy disk unit 1 is so constructed that themedium 2 is loaded with its longitudinal axis or center line deviated inthe direction of an arrow B, which is substantially at a right angle tothe loading direction A of the medium 2, from the center line of thewidth W of the unit, and the empty space 10 is formed between the medium2 and the chassis 3. And, the support plate 6 extends into the emptyspace 10, and an adjustment portion for effecting timing adjustment ofindex signal or, in the embodiment, a variable resistor 25 is mounted onthe extended portion of the support plate. That is, the variableresistor 25 is disposed at a position where it is prevented fromoverlapping the alignment medium 2 inserted through the insertionentrance 5 as viewed in a plan. The timing adjustment may be effected inany way and, for example, the variable resistor 25 serves to effect thetiming adjustment of index signal by changing the reference voltage,varying the output voltage or changing the time constant.

Since the variable resistor 25 is so arranged as not to overlap theloaded medium 2 as viewed in a plan, even when an adjusting tool or, forexample, a screw driver is inserted from above, it can be engaged withthe variable resistor 25 easily without interfering with the loadedalignment medium 2.

Description will be made on the operation of timing adjustment of indexsignal in the embodiment.

The floppy disk unit 1 finished through the manufacturing line is put ona pallet (not shown), and the alignment medium 2 is loaded through theinsertion entrance 5 into the unit 1 in this state as indicated by thearrow A. On the recording disk of the medium 2 are written not only thesignals for radial adjustment (alignment adjustment) and head gapadjustment (azimuth adjustment) of the magnetic heads 17, 18 but alsothe signal for adjusting the rotating position from the physicalreference point to the head gap (index burst signal). Subsequently,connecting pins (not shown) are lowered to be connected to connectionterminals of the unit (not shown) so as to supply the necessary electricpower and signals. Then, the spindle motor 7 is operated to rotate therecording disk of the medium 2, and the stepping motor 20 is operated torotate the lead screw 21, so that the carriage 13 and the head arm 15are moved in the radial direction of the recording disk to move thefirst and second magnetic heads 17, 18 to the desired track where theindex burst signal is written. The magnetic heads 17, 18 magneticallyread out the signal from the medium 2 and send the read-out signal to asignal processing circuit (not shown) via a read circuit (not shown),the connection terminals and the connecting pins. The adjusting screwdriver is inserted from above and engaged with the index adjustmentvariable resistor 25, and the adjustment is carried out in accordancewith the read-out signal.

As described above, in adjusting the variable resistor, the adjustingtool such as the screw driver can be engaged with the variable resister25 from above easily and reliably without involving such a precise anddifficult operation that it is engaged with the volume from the back ofa base plate through a small hole formed therein for adjustment. Sinceall of the operations required for the timing adjustment of the indexsignal can be carried out from above alone, the embodiment describedabove has many advantages from the viewpoints of facilities, accuracyand cost. Further, the floppy disk unit 1 of this embodiment can berealized with the width W thereof kept as equal as that of theconventional unit since it is constructed such that the alignment medium2 is loaded to be offset in the direction of the arrow B.

Further, according to the embodiment, by boring the fitting hole 60 inthe support plate 6 by means of press work and by caulking the ring-likecaulking portion 73 formed integrally with the bearing member 70, themember 70 can be fixed to the support plate 6. The holding forcerequired for the sizing work can be produced at the caulking portion andpress-fitting is not required, so that the bearing member can be reducedin height. By setting adequately the relationship between the dimensionsof the caulking portion 73 to be filled in the void space 62 and theamount of shear droop of the portion 61, the lower surface of thebearing member 70 becomes substantially flush with the lower surface ofthe support plate 6, and substantially no projecting portion is formed.Accordingly, it is possible to reduce the overall thickness of the unitall the more. Moreover, since no screw is required to fix the member 70,the number of working steps and the number of component parts can bedecreased, thereby making it possible to reduce the cost and weight.

In addition, since the inner peripheral surface of the ring-likecaulking portion 73 of the bearing member 70 is inclined at an acuteangle with respect to the outer peripheral surface thereof, the caulkingportion 73 is caulked relatively easily to fill up the void space 62with reliability.

Besides, although in the above-described embodiment the medium is offsetto the right of the chassis 3 in FIG. 1, it may be located close to theleft as well. In this case, the head positioning device 12, the variableresistor 25 and so forth are arranged in the empty space 10 on theright. In case that the empty space 10 is formed along the side of thechassis 3 and the device 12, the variable resistor 25 and the like arearranged in this empty space like the above-described embodiment, thereis an advantage that the overall size of the floppy disk unit 1 can bemade smaller through a reduction in the depth thereof. However, if thedepth is not limited, the variable resistor 25, the head positioningdevice 12 and the head support device 11 may be arranged in the back ofthe unit 1 as well. In the above-described embodiment, the medium andthe variable resistor 25 are prevented from overlapping each other asviewed in a plan by making use of the empty space 10 formed in thewidthwise direction, and however, such arrangement can be realizedlikewise in other direction than the widthwise direction. Further, theadjustment portion is not limited to the variable resistor 25 but may beany device that it is adjustable. For example, a switch, a trimmercondenser, a device for selecting a resistance by means of a short plugor the like, or a device for effecting the trimming by means of a lasermay be alternatively used. In other words, any form or method can beavailable.

Description will be now made on a floppy disk unit according to thesecond embodiment of the invention. Component elements of the secondembodiment, which may be the same with those of the aforesaidembodiment, are designed by the same reference numerals, and descriptionthereof will be omitted.

FIGS. 4 to 6 show the essential portions of a bearing for a spindlemotor in the second embodiment. Also in this embodiment, a support plate6 is formed therein with a fitting hole by means of press work so that ashear-droop portion 61 is formed along the periphery of the fitting holeof the support plate. The support plate 6 is formed on the upper surfacethereof with a printed circuit board (PCB) 26. A bearing member 170 ismade of a copper-base sintered alloy and is generally in a steppedcylindrical shape that is provided in its upper part with a largediameter portion 171 which has an outside diameter larger than thediameter of the fitting hole of the support plate, and with a smalldiameter portion 172 which is to be fitted in the fitting hole of thesupport plate. Further, similarly to the first embodiment, a ring-likecaulking portion 173 is formed at the lower end of the small diameterportion 172, and a through hole 174 is formed in the center of thebearing member. In addition, in the large diameter portion 171, abearing fitting hole 175 that has an diameter larger than that of thethrough hole 174 is formed concentrically with the through hole 174, sothat the bearing member 170 serves as a bearing housing as well.

The bearing member 170 is fixed to the support plate 6 with thering-like caulking portion 173 caulked radially outwardly to fill up agap or void space 62 (see FIG. 5) between the small diameter portion 172and the shear-droop portion 61, similarly to the case of the firstembodiment. Moreover, in the second embodiment, a ball bearing 27 ispress-fitted in the fitting hole 175 and the outer race thereof is fixedthereto. A rotary shaft 8 is rotatably supported by the ball bearing 27and the hole 174 of the bearing member 170.

In the embodiment, since the bearing member 70 serves as the bearinghousing as well, the member 70 is large in external shape. In otherwords, the hole 174 for supporting the rotary shaft 8 is distant fromthe ring-like caulking portion 173. As a result, the hole 174 is hardlydeformed even in caulking work, thereby making it possible to omit thesizing work which has been indispensable in the prior art for attainingthe required dimensions. This embodiment is applicable to the case wherethe length over which the bearing member is fixed to and held by thesupport plate is too short to effect the sizing after the press-fitting.Further, in case of requiring the sizing, even when the thickness of thebearing member is small, the bearing member can be firmly fixed to thesupport plate 6 through the caulking, and a holding force large enoughto withstand the torque needed for the sizing is produced. Additionally,it is possible to mount parts for controlling the motor and the like onthe printed circuit board 26 and, accordingly, the number of componentparts of the unit can be reduced to thereby simplify the structure ofthe unit.

The inventor produced the above-described bearing portion by way oftrial and took a photograph of the cross section of a part thereofindicated by reference character E in FIG. 4 after effecting thecaulking. FIG. 6 shows an illustration from the enlarged photograph(×17) thus taken.

In the trial production, an iron plate was used as the support plate 6,the thickness of the iron plate was 0.6 mm and the diameter (at thestraight portion) of the fitting hole 60 was 14 mm. The bearing member170 was made of a copper-base sintered alloy NY-105, product of NIPPONKAGAKU YAKIN Co., Ltd. The diameter of the through hole 174 of thebearing member was about 4 mm and the dimensions of the ring-likecaulking portion 173 were 1 mm in width, 60 degrees in inclination α and0.7 mm in height. Further, a US-1 MODEL caulking machine, product ofYOSHIKAWA IRON WORKS Co., Ltd., was used at an air pressure of 3 Kg/cm²to caulk the ring-like caulking portion 173.

FIG. 6 clearly shows the state that the ring-like caulking portion 173is filled in the gap 62. After the caulking, the ring-like caulkingportion 173 projected downward beyond the support plate 6 only by 0.1 mmso that the lower surface of the support plate 6 and the lower end ofthe bearing member 170 were substantially flush with each other. It willbe clearly seen from FIG. 6 that the bearing member 170 is fixed withsubstantially no projecting portion formed. Concerning the through hole174 of the bearing member, no change was observed in the inside diameterthereof before and after the caulking work. Further, the length overwhich the bearing member is held was as well as about 0.06 mm, but aforce of about 20 Kg was required to extract the bearing member, andaccordingly, the holding force according to the invention was improvedby about four times as compared with an extracting force of about 5 Kgfor the conventional press-fitting.

The second embodiment has the following advantages in addition to theadvantages of the first embodiment described before. When the supportplate 6 is made of magnetic material such as iron or silicon steelplate, the support plate can be used as a back yoke of the motor.Further, when the support plate is formed by iron PCB or silicon PCBwhich is provided with the printed circuit board, the magnetic circuitand the electric circuit of the motor can be realized as one body, andaccordingly, the number of component parts of the unit can be reduced.Since the bearing member 170 is made of a copper-base sintered alloy andis formed in the upper part thereof with the fitting hole 175 for theball bearing, it is possible to disuse a separate bearing housing and,moreover, it is possible to enjoy the each of caulking and the excellentcharacteristics of the bearing to the rotary shaft made of stainlesssteel. The bearing member of copper-base sintered alloy is generallyburned at a lower temperature than that required for iron-base sinteredalloy so that the accuracy of the dimensions can be obtained easily, theaccuracy of the degree of concentricity between the bearing fitting hole175 and the through hole 174 can be increased and hence the accuracy ofthe bearing can be improved.

Although the second embodiment has been described in regard to thebearing portion alone, the other portions of the unit may be the same asthose of the first embodiment. Incidentally, as seen from the foregoingdescription, the improvements of the adjustment portion and the bearingportion according to the invention may be applied independently of eachother.

The invention has been described above in conjunction with theembodiments, and however, it should be appreciated that the invention isnot limited solely to these specific forms and various changes andmodifications can be made to the described forms or the invention can beembodied in other forms without departing from the scope of the appendedclaims.

What is claimed is:
 1. A floppy disk unit for rotating a medium loadedthereon to read and write information, comprising:bearing means forrotatably supporting the medium, said bearing means including a bearingmember made of a sintered alloy, said bearing member having an endportion; and a metal support plate having a through hole formed therein,said end portion of said bearing member being fitted in said throughhole and having a band-like projection projected out from one surface ofsaid support plate, said through hole having a large diameter portionlarger in diameter than other portions thereof along an opening of saidthrough hole in said one surface so that said large diameter portionprovides, between said through hole and said end portion of said bearingmember fitted therein, a gap in which said band-like like projection iscaulked to fill said gap and to fix said bearing member to said supportplate; wherein said large diameter portion of said through hole is ashear-group portion caused when said through hole is formed by presswork; and wherein said gap has a size that makes said band-likeprojection after being caulked and said one surface of said supportplate substantially flush with each other.
 2. A unit according to claim1, wherein said end portion of said bearing member has a flat surfacewhich is made substantially flush with said one surface of said supportplate when said bearing member is fixed to said support plate.
 3. A unitaccording to claim 1, wherein said end portion of said bearing memberhas a cylindrical shape, and said band-like projection is shaped like aring and has an outer peripheral surface which is coextensive with anouter periphery of said end portion of said bearing member and an innerperipheral surface which is inclined at an acute angle with respect tosaid outer peripheral surface.
 4. A unit according to claim 1, whereinsaid support plate comprises a base member made of magnetic material anda circuit board which is combined with said base member to provideanother surface on an opposite side of said support plate to said onesurface thereof.
 5. A unit according to claim 4, wherein said magneticmaterial is one of iron and silicon steel.
 6. A unit according to claim1, further comprising:a chassis defining an outer contour of the unitand receiving therein said bearing means and said support plate; rotarydriving means loaded in said chassis for rotating the medium and adaptedto be positioned below the medium; magnetic head means provided in saidchassis movably with respect to the medium for reading and writinginformation from and to the medium; and adjust means for adjusting aposition of said magnetic head means with respect to the medium, saidadjust means being arranged in said chassis so that said adjust means isprevented from being overlapped by the medium when the medium is loadedin the unit and is engaged with said rotary driving means, so that saidadjust means is accessible from above.